Summary The sense of touch provides critical information about our physical environment by transforming mechanical energy into electrical signals1. It is postulated that mechanically activated (MA) cation channels initiate touch sensation, but the identity of these molecules in mammals has been elusive2. Piezo2 is a rapidly adapting (RA) MA ion channel expressed in a subset of sensory neurons of the dorsal root ganglion (DRG) and in cutaneous mechanoreceptors known as Merkel cell-neurite complexes3,4. Merkel cells have been demonstrated to play a role in vertebrate mechanosensation using Piezo2, particularly in shaping the type of current sent by its innervating sensory neuron4-6. However, major aspects of touch sensation remain intact without Merkel cell activity4,7. Here, we show that mice lacking Piezo2 in both adult sensory neurons and Merkel cells exhibit a profound loss of touch sensation. We precisely localize Piezo2 to the peripheral endings of a broad range of low threshold mechanoreceptors (LTMRs) that innervate both hairy and glabrous skin. Most RA MA currents in DRG neuronal cultures are absent in Piezo2CKO mice, and ex vivo skin nerve preparation studies show that mechanosensitivity of LTMRs strongly depends on Piezo2. This striking cellular phenotype correlates with an unprecedented behavioral phenotype: an almost complete deficit in light touch sensation in multiple behavioral assays, without affecting other somatosensory functions. Our results highlight that a single ion channel that displays RA MA currents in vitro is responsible for the mechanosensitivity of most LTMR subtypes involved in innocuous touch sensation. Interestingly, we find that touch and pain sensation are separable, suggesting that yet-unknown MA ion channel(s) must account for noxious (painful) mechanosensation.

Summary The high rate of clinical response to protein kinase-targeting drugs matched to cancer patients with specific genomic alterations has prompted efforts to use cancer cell-line (CCL) profiling to identify additional biomarkers of small-molecule sensitivities. We have quantitatively measured the sensitivity of 242 genomically characterized CCLs to an Informer Set of 354 small molecules that target many nodes in cell circuitry, uncovering protein dependencies that: 1) associate with specific cancer-genomic alterations and 2) can be targeted by small molecules. We have created the Cancer Therapeutics Response Portal (www.broadinstitute.org/ctrp) to enable users to correlate genetic features to sensitivity in individual lineages and control for confounding factors of CCL profiling. We report a candidate dependency, associating activating mutations in the oncogene β-catenin with sensitivity to the Bcl2-family antagonist, navitoclax. The resource can be used to develop novel therapeutic hypotheses and accelerate discovery of drugs matched to patients by their cancer genotype and lineage.

Inhibitors of histone deacetylases (HDACs) induce growth arrest, differentiation, and apoptosis of colon cancer cell lines in vitro and have demonstrated anti-cancer efficacy in clinical trials. Whereas a role for HDAC1 and -2 in mediating components of the HDAC inhibitor response has been reported, the role of HDAC3 is unknown. Here we demonstrate increased protein expression of HDAC3 in human colon tumors and in duodenal adenomas from Apc1638 N/؉ mice. HDAC3 was also maximally expressed in proliferating crypt cells in normal intestine. Silencing of HDAC3 expression in colon cancer cell lines resulted in growth inhibition, a decrease in cell survival, and increased apoptosis. Similar effects were observed for HDAC2 and, to a lesser extent, for HDAC1. HDAC3 silencing also selectively induced expression of alkaline phosphatase, a marker of colon cell maturation. Concurrent with its effect on cell growth, overexpression of HDAC3 and other Class I HDACs inhibited basal and butyrate-induced p21 transcription in a Sp1/Sp3-dependent manner, whereas silencing of HDAC3 stimulated p21 promoter activity and expression. However, the magnitude of the effects elicited by silencing of individual Class I HDACs was significantly less than that induced by HDAC inhibitors. These findings identify HDAC3 as a gene deregulated in human colon cancer and as a novel regulator of colon cell maturation and p21 expression. These findings also demonstrate that multiple Class I HDACs are involved in repressing p21 and suggest that the growthinhibitory and apoptotic effects induced by HDAC inhibitors are probably mediated through the inhibition of multiple HDACs.Acetylation of DNA-bound core histones and sequence-specific transcription factors is a fundamental mechanism of transcriptional regulation. Histone acetylation is typically associated with increased transcription (1) and is regulated by two opposing classes of enzymes: histone acetyltransferases, which add acetyl groups to specific amino acids of the histone protein, and histone deacetylases (HDACs), 2 which catalyze their removal. A second mechanism by which HDACs may regulate gene transcription is by regulating acetylation of DNA sequence-specific transcription factors. Examples include p53, E2F, and Sp3, where deacetylation has been linked to reduced DNA binding or transcriptional activity (2-4). Through these mechanisms, HDACs are emerging as critical regulators of cell growth, differentiation, and apoptotic programs. We and others have demonstrated that inhibitors of HDACs, such as sodium butyrate, trichostatin A (TSA), suberoylanilide hydroxamic acid (SAHA), and valproic acid, induce cell cycle arrest, differentiation, and apoptosis in colon cancer cell lines in vitro (5-10). These observations suggest a physiological role for transcriptional repression mediated by HDACs in maintaining cell proliferation and survival and inhibiting differentiation. Correspondingly, the deregulation of HDAC-mediated transcriptional repression has been linked to tumorigenesis. The up-regulated e...

Artificial photosynthesis relies on the availability of synthetic photocatalysts that can drive CO reduction in the presence of water and light. From the standpoint of solar fuel production, it is desirable that these photocatalysts perform under visible light and produce energy-rich hydrocarbons from CO reduction. However, the multistep nature of CO-to-hydrocarbon conversion poses a significant kinetic bottleneck when compared to CO production and H evolution. Here, we show that plasmonic Au nanoparticle photocatalysts can harvest visible light for multielectron, multiproton reduction of CO to yield C (methane) and C (ethane) hydrocarbons. The light-excitation attributes influence the C and C selectivity. The observed trends in activity and selectivity follow Poisson statistics of electron harvesting. Higher photon energies and flux favor simultaneous harvesting of more than one electron from the photocharged Au nanoparticle catalyst, inducing the C-C coupling required for C production. These findings elucidate the nature of plasmonic photocatalysis, which involves strong light-matter coupling, and set the stage for the controlled chemical bond formation by light excitation.